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Days within a study may be represented relative to the reference start date represented in variable RFSTDTC or in relation to applicant-defined reference dates.



The SDTM allows for the representation of study days relative to the RFSTDTC reference start date variable in the DM dataset, using variables --DY, as described in Section 4.4.4, Use of the "Study Day" Variables. The calculation of additional study days within subdivisions of time in a clinical trial may be based on 1 or more sponsor-defined reference dates not represented by RFSTDTC. In such cases, the sponsor may define supplemental qualifier variables and the Define-XML document should reflect the reference dates used to calculate such study days. If the sponsor wishes to define "day within element" or "day within epoch", the reference date/time will be an element start date/time in the Subject Elements (SE) dataset (see Section 5.3, Subject Elements).


NumVariable PopulationImplementation

Study Days in Relation to the Study Reference Date(--DY, --STDY, --ENDY)

Variables --DY, --STDY, and --ENDY represent days relative to the reference start date in RFSTDTC where:

  • --DY is the relative study day of the date populated in --DTC for the observation,
  • --STDTC is the relative study day of the date populated in --STDTC for the observation; and
  • --ENDY is the relative study day of the of the date populated in --ENDTC for the observation.

All study day values will be integers and there will be no study day 0. The reference start date is considered day 1 and the study day value is increased by 1 for each date following the reference start date and decreased by 1 for each date prior to the reference start date, e.g.:

--DY = (date portion of --DTC) - (date portion of RFSTDTC) + 1 if --DTC is on or after RFSTDTC
--DY = (date portion of --DTC) - (date portion of RFSTDTC) if --DTC precedes RFSTDTC

Study Days
  • Study days may be cal


The calculation of additional study days within subdivisions of time in a clinical trial may be based on 1 or more sponsor-defined reference dates not represented by RFSTDTC. In such cases, the sponsor may define supplemental qualifier variables and the Define-XML document should reflect the reference dates used to calculate such study days. If the sponsor wishes to define "day within element" or "day within epoch", the reference date/time will be an element start date/time in the Subject Elements (SE) dataset (see Section 5.3, Subject Elements).










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